Greece is on the brink of a severe healthcare crisis as shortages of medicines are exacerbated by panic among patients unable to get cancer or cardiac drugs, pharmacists have warned.

The insolvent country's worsening liquidity has led to public insurers being unable to pay bills and prescription drugs running dangerously low, say chemists. On Wednesday, the sector staged a one-day strike to highlight the "emergency situation".

"I give it 15 days. If the European Union doesn't release the loans it has promised by then, there will be scenes of utter chaos here," said Dimitris Karageorgiou, secretary general of the Panhellenic Pharmaceutical Association.

"The situation will become dramatic. Already we have cancer sufferers going from hospital to hospital to try and find drugs because no one can afford to stock them," he said. "If the shortages get worse, God knows what we will see."

The effects of the twice bailed-out nation's internationally mandated scramble to rein in runaway public debts have been felt across the board in the last month as concerns have grown over Athens' ability to remain in the eurozone.

"In that time 120 pharmacies have closed in Athens alone because of pressures from delays in payments for prescriptions from social security funds," said Karageorgiou. "Whatever you read about shortages is little. There are about 300 medicines that are no longer readily available. It's tragic."

Seated in her pharmacy in Plaka, the ancient district beneath the Acropolis, Mary Papazoglou said shortages ranged from antibiotic creams to thyroid and heart drugs.

"The situation with anti-cancer drugs is out of control but what can we do?" she said. "Because we're not being reimbursed we can't pay suppliers who can't pay the companies. It's a chain effect."

Under pressure from its "troika" of international creditors at the EU, European Central Bank and International Monetary Fund, Athens amalgamated 13 social security funds into one body – the National Organisation for Healthcare Provision (EOPYY) – after being first propped up with rescue loans in May 2010.

But the pharmaceutical association, with 12,000 members, says the funds were unified "so violently" in the space of a year, with donations either not forthcoming or drying up completely, that NOPF quickly collapsed.

A fifth straight year of recession, which will have seen the Greek economy contract by around 27% by the end of 2012, had also had a devastating effect, said Karageorgiou.

"Record unemployment and mass emigration has meant that there is very little money coming into the funds," he said. "There is also a lot of confusion. In 2011 a total of 17 insurance laws were passed in parliament and they were often contradictory. The result has been no money in the till."

Pharmacists are owed about €1bn (£800m) by health insurers, say sector officials. As a result of the failure of state funds to cover prescription payments, chemists had, they said, been forced to no longer dispense drugs on credit. Instead, as of this week, patients will have to pay up front before being reimbursed from the state. Karageorgiou said: "You tell me. How can a pensioner surviving on little more than €400 a month afford cancer medications that cost €380?""This is the mess that lack of foresight has got us in."

Greece's cashflow problem has been exacerbated by the inconclusive elections on 6 May. As the country heads to polls again on 17 June, it does so under the threat of further rescue funds being withheld until a new government, ready to commit to unpopular reforms in return for aid, is in place in Athens.

Amid growing alarm, global drug companies have begun drawing up contingency plans to keep medicines flowing into the country in the event of it exiting the eurozone. Most of Greece's drug supplies are imported from abroad. Greek officials say part of the "nightmare" scenario that would ensue if Athens were to return to the drachma would involve the nation being unable to afford drug and medicine imports after any huge devaluation of the newly minted currency.